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Physical Anthropology > Human Pigmentation > Flashcards

Human Pigmentation Flashcards

1
Q

Plasticity/Adaptability

A

The ability of an individual organism to short-term make physiological changes in response to exposure to stressful environmental conditions

  • often associated with changes that come to be over the period of growth and development
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2
Q

Adaptation

A

The ability of an individual organism to make anatomical or physiological changes in response to exposure to stressful environmental conditions

  • often associated with changes that come to be by altering patterns of growth and development
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3
Q

Acclimatization

A

State reverts after environmental stress is removed

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4
Q

What is the largest organ of the body?

A

Skin
- our most conspicuous polymorphism

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5
Q

The many functions of Skin:

A
  • protection
  • thermoregulation
  • Vitamin D synthesis
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6
Q

What is the pigment primarily responsible for light-dark coloration of most animals?

A

Melanin

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7
Q

All people have the same number of Melanocytes, but what are melanocytes?

A

Cells that make melanin

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8
Q

Skin color depends on how much and which type of _____ is produced

A

Melanin

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9
Q

Eumelanin

A

molecule responsible for most variation in human skin pigmentation
- Dark: Brown to black
- Concentration accounts for skin’s darkness

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10
Q

Pheomelanin

A
  • Lighter: yellow to reddish brown
  • Accounts for skin’s reddish-brown color
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11
Q

Lightly pigmented people are while (the color of connective tissue)

A

A pink hue comes from blood hemoglobin showing through

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12
Q

Our skin has a layer structure. Melanocytes are near the base of the epidermis

A
  • Melanocytes are embedded between the basal layer and the overlying stratum spinosum
  • As melanosomes fill up with melanin, the pigment gets distributed to new skin cells through the dendrites
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13
Q

Skin pigmentation is determined by:

A
  • rate of production
  • distribution
  • size of melanin packets
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14
Q

There are a lot of biological factors involved in melanin and skin pigmentation

A
  • some are genetic
  • some are hormonal
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15
Q

Are all babies born with lighter skin than they will have as adults?

A

Yes; because melanocytes have to “ramp up” into production

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16
Q

Human biologists measure skin color using spectrophotometers or similar equipment

A

This measures how much light is reflected at a specific wavelength
- light colors reflect more light
- darker colors absorb more light

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17
Q

Human skin pigmentation is an excellent example of a continuous and complex phenotype

A
  • skin pigmentation is highly polymorphic
  • continuous: the polymorphisms have gradient-style variation (there are an infinite number of intermediate states)
  • complex phenotypes are influenced by environment (genetic-adaptation=constitutive pigmentation; acquired-acclimatization=facultative pigmentation)
  • skin pigmentation is polygenic (many genes)
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18
Q

Is skin pigmentation highly heritable?

A

Yes
- BUT the genetic control over the phenotype is not straightforward

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19
Q

The TYR gene makes the enzyme tyrosinase, which is involved in _____?

A

melanin production at a few different stages

20
Q

Albinism

A

caused by the lack of melanin
- over 100 distinct genetic causes/mutation in TYR

21
Q

4-6 genes identified for skin pigmentation genetics?

A

1.) TYR: Tyrosinase
2.) MC1R: Melanin production
3.) OCA2: P protein, has to do with melanosome function
4.) OCA4
5.) SLC24A5

Same reflectance value from different genotypes
- some alleles can be MASKED

22
Q

Some genes involved in skin pigmentation are also involved in eye and hair color

A

Melanin is also involved in eye color
- eye darkness vs. lightness

OCA2 (Chromosome 15) was identified by earliest studies to be the dominating factor for eye color determination
- now known that other genes are involved (HERC2) that don’t affect melanin directly

MCR1 contains regions where the allele present is associated with whether or not a person has green eyes

TYR can stop melanin production at the highest hierarchical level

23
Q

UVR

A

Energy with wavelength between visible light and x-rays
- has potential to alter biological processes

24
Q

UVR can be sub-divided into:

A

UVA: longest wavelength, potential to penetrate skin deeply
UVB: intermediate wavelength, potential to penetrate skin less deeply
UVC: shortest wavelength, atmosphere absorbs/scatters

25
Q

More and larger melanosomes permit___

A

less UVR penetration

26
Q

Darkest human pigmentation can block ca. 95% UVR

A

Light pigmentation blocks less than 50% UVR

27
Q

UVR negative effects

A
  • UVR can damage the skin
  • sunburn (caused especially by UVB)
  • destroys skin elasticity (UVA)
  • can damage molecules and compounds inside the body
  • all UV wavelengths can damage DNA
  • This is one cause of melanoma
28
Q

Short-term, reversible response to UVR penetration

A

Tanning

29
Q

Tanning

A

When UVR exposure exceeds a threshold, your body starts a self-regulation mechanism
- existing melanin skin darks (UVA)
- melanin production is increased (UVB) (at this point, you already have DNA damage)

30
Q

All people can tan. All people can burn.

A

TRUE; the amount you see the different will depend on how dark someone is

31
Q

Folate (folic acid)

A

B vitamin required to produce nucleic acids
- an process involving cell proliferation

Linked to many birth defects
- plays an important role n brain and spinal cord

Required for spermatogenesis

Myelin and serotonin
- brain function

32
Q

Positive effects of UVR

A

Catalyze production of compounds inside the body

Vitamin D synthesis
- UVB exposure initiates pre-vitamin D production

33
Q

UVR intensity varies with latitude and altitude

A

TRUE

34
Q

Earth is a sphere

A

Cross-sectional area of “a ray of sunlight” increases with distance from equator

Earth has a thick atmosphere that absorbs and scatters UVR
- a ray of sunlight hitting surface at equator passes through less atmosphere than one hitting surface at high latitude
- altitude alos affects UV intensity for this reason

Intensity of UV radiation increases near equator, and creates at high altitude localities near equator

35
Q

Human populations living in some parts of the world are at risk of UVR overexposure while…

A

others are at risk of underexposure

36
Q

At high latitudes

A

Season affects UVR
- each currently has an axial tilt of about 23 degrees
- Axial tilt accounts for variation in length of daylight (near the equator, there is no significant variation in day length throughout)

37
Q

Overexposure risk in the summer and underexposure risk in the winter example

A

True

38
Q

There is a very strong correlation between pigmentation and UVR strength… how? Why?

A

Pigmentation in the skin serves as a natural defense mechanism against the harmful effects of UV radiation. The darker the skin, the more melanin present, providing greater protection against sun damage

39
Q

Non-human apes are lightly pigmented under their hair (they have little melanin in their skin)

A
  • they can develop facultative pigmentation on their more exposed areas
  • or exposed areas are permanently pigmented
40
Q

The evolution of darkly pigmented skin is probably linked to hairlessness

A
  • responses to increased temperature regimes with expansion into shadeless environments
  • hair prevents effective evaporative cooling
41
Q

When did hominins get naked?

A

When they moved into shadeless environments
- sometime near the beginning of the Pleistocene

Homo erectus
- shows adaptation to hot environments in body proportions
- associated with dry and open grassland fauna
- researchers propose that the species was dark and naked

42
Q

How would darkly pigmented skin have contributed to differential fitness?

A

Proposed hypotheses:
- sunburn
- folate protection
- skin cancer

43
Q

The folate hypothesis

A

Argues that protection of folate stores enhanced fitness of early hominins with darkly pigmented skin
- folate depletion in females is associated with the development of neural tube defects in the fetus
- darkly pigmented women have lower incidence of neural tube related birth defects
- there is an annual peak of babies born with neural tube defects that were conceived in the summer months
- in men, folate deficiency is associated with impaired spermatogenesis

44
Q

How would lightly pigmented skin have contributed to differential fitness?

A
  • Darwin thought it was sexual selection
  • increased vitamin D synthesis
45
Q

Support for the Vitamin D hypothesis

A

Vitamin D and bone formation
- Calcium absorption
- osteoblast and chondrocyte activity
- can lead to rickets

Vitamin D vital to immune system function

Independent evolution of lightly pigmented skin
- molecular signature of purifying selection

Physical Anthropology (18 decks)

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